The collision took place at 7pm just after junction 12 (Talybont), near Bangor, Gwynedd.

The road was closed for more than an hour betweenTalybont and Llandegai. Eyewitness Rob Jones said: “There were police and ambulance there and a lot of damaged vehicles being shunted on to recovery trucks.”

A Traffic Wales spokesman said there were diversions in operation between the two junctions and that the collision had caused long tailbacks.

Just before the A55 crash, there was another collision which closed the A4086, Llanberis Road in Caernarfon.

That caused heavy traffic in both directions between Bethel Road on the Lon Ysgol Rad junction, because of accident investigation work.